Fuel injection system and method for injection

ABSTRACT

A fuel injection system ( 1 ) for internal combustion engines has at least one fuel injector ( 7 ) which injects fuel into a combustion chamber ( 6 ) delimited by a cylinder wall ( 2 ) in which a piston ( 3 ) is guided, and it has a spark plug ( 8 ) which protrudes into the combustion space ( 6 ), and the fuel injector ( 7 ) is designed so that a conical spray jet ( 13 ) is produced in the combustion chamber ( 6 ). The conical spray jet ( 13 ) has an angle cutout ( 17 ) in the area of the spark plug ( 8 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a fuel injection systemaccording to the definition of the species of claim 1 and a method ofinjection according to the definition of the species of claim 11.

[0002] In internal combustion engines having spark ignition of acompressed fuel mixture with internal formation of the mixture, a“mixture cloud” which must have a certain fuel-air ratio in theignitable range is required for stratified charge operation in the sparkplug area. To this end, fuel injectors having nozzles which open towardthe inside or the outside and produce a conical jet are used.

[0003] For example, German Patent Application 198 04 463 A1 describes afuel injection system for internal combustion engines having sparkignition of a compressed fuel mixture; this fuel injection system isprovided with at least one fuel injector which injects fuel into acombustion chamber formed by a piston/cylinder arrangement and isequipped with a spark plug projecting into the combustion chamber. Thefuel injector is provided with at least one row of injection holesdistributed over the circumference of a nozzle body of the fuelinjector. Through controlled injection of fuel through the injectionholes, a jet-guided combustion method is implemented by the formation ofa mixture cloud, at least one jet being directed in the direction of thespark plug. Other jets ensure that an at least approximately closed orcoherent mixture cloud is formed.

[0004] German Patent 196 42 653 C1 describes a method of forming anignitable fuel-air mixture. An ignitable fuel-air mixture is formable inthe cylinders of direct injection internal combustion engines, in thatfuel is injected into each combustion chamber delimited by a piston, byway of an injector on opening of a nozzle orifice due to a valve elementbeing lifted up from a valve seat surrounding the nozzle orifice. Topermit formation of a mixture optimized for fuel consumption andemissions in each operating point of the entire engine characteristicsmap under all operating conditions of the internal combustion engine, inparticular in stratified charge operation, the opening stroke of thevalve element and the injection time are adjustable.

[0005] German Patent 38 08 635 C2 describes a fuel injection device fordirect injection of fuel into the cylinder of an internal combustionengine having compression of a fuel mixture. The fuel injection deviceincludes a fuel injector which is situated in the cylinder wall at adistance from the cylinder head and opposite the exhaust opening andwhich has an outlet opening, with the axis of the jet of the injectionvalve being directed at the area around the spark plug situated in thecylinder head. The fuel injector here has a magnetically operated valveneedle having helical swirl grooves to produce a swirl flow of theinjection jet. The total cross-sectional area of the swirl grooves issmaller by at least one half than the cross-sectional area of the outletopening, the fuel injector being situated above the flushing opening,and with its jet axis directed at the ignition point situated at thecenter of the cylinder head.

[0006] Most injection systems known from the publications cited aboveconcern combustion methods with wall-guided fuel flow. This combustionmethod depends to a very great extent on the movement of incoming airwhich has the function of conveying an ignitable fuel-air mixtureexactly into the electrode area of the spark plug over the entirestratified charge operation range of the engine characteristics map. Inthe wall-guided combustion method, fuel is carried to the spark plugwith the support of more or less fractured combustion chamber geometrieswith simultaneous formation of the mixture.

[0007] Transport of the mixture to the spark plug is very incomplete inwall-guided and air-guided combustion methods in idling operation and inthe lower partial load range, and in the middle partial load range ofoperation, it is possible in part only with unjustifiably lowmanufacturing tolerances of the high-pressure injectors used or the flowguidance through the intake manifold. The inadequate reproducibility isapparent in particular in increased emission of unburned hydrocarbonsdue to isolated instances of misfiring. These properties result inanother serious disadvantage of the two combustion methods mentionedabove: the engine cannot be operated unthrottled in the idling and lowerpartial load ranges because due to the great distance between the fuelinjector and the spark plug, smaller injection quantities no longerreach the spark plug in the mixture concentration required for stablecombustion. This means that the fuel-air mixture at the spark plugelectrodes becomes too lean. However, the consumption advantage isreduced in comparison with internal combustion engines havingcompression of a mixture with spark ignition and intake manifoldinjection due to the intake air throttling.

ADVANTAGES OF THE INVENTION

[0008] The fuel injection system according to the present inventionhaving the characterizing features of claim 1 and the method accordingto the present invention having the characterizing features of claim 11have the advantage over the related art that the mixture in the area ofthe spark plug is not too rich due to the angle cutout.

[0009] It is also advantageous that the spark plugs do not develop asmuch soot, thermal shock load is reduced, and there is an improvement inthe lack of sensitivity to the firing angle with a fixed injection timein the entire engine characteristics map in which stratified chargeoperation is carried out. Injection and ignition (or vice versa) maytake place simultaneously.

[0010] It is also advantageous that the spark cannot be blown out due tothe high injection rate because the droplet speed is greatest at thecenter of the jet, and on the angle bisectors of the two injection jetsbordering the spark plug area, the spark conforms exactly torequirements regarding the quality of the fuel-air mixture and the rateof flow.

[0011] It is also advantageous that the depth of installationsensitivity of the spark plug is lower.

[0012] Advantageous refinements of the fuel injection systemcharacterized in claim 1 are possible through the measures characterizedin claims 2 through 10.

[0013] The injection jet is advantageously formed using a plurality ofinjection holes. Injection holes may be situated to advantage in severaloffset rows.

BRIEF DESCRIPTION OF THE DRAWING

[0014] Embodiments of the present invention are illustrated in thedrawing in simplified form and explained in greater detail in thefollowing description.

[0015]FIG. 1 shows a schematic axial section through an embodiment of afuel injection system according to the present invention,

[0016]FIG. 2 shows the section labeled as II-II in FIG. 1 through thecylinder head of the embodiment of the fuel injection system accordingto the present invention as illustrated in FIG. 1,

[0017]FIG. 3 shows a schematic diagram of a first jet pattern producedby the fuel injection system according to the present invention,

[0018]FIGS. 4A and 4B show a schematic diagram of a second jet patternproduced by another embodiment of the fuel injection system according tothe present invention, and

[0019]FIG. 4C shows the arrangement of injection holes to produce thejet patterns,

[0020]FIG. 5A-C show diagrams of the emissions of hydrocarbons andnitrogen oxide and the specific fuel consumption, each shown for a fuelinjection system with and without the angle section according to thepresent invention for the spark plugs.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021]FIG. 1 shows a detail of a sectional diagram of one embodiment ofthe fuel injection system according to the present invention.

[0022] Fuel injection system 1 includes a cylinder block having acylinder wall 2 in which a piston 3 is guided. Piston 3 is guided up anddown by a connecting rod 4 on cylinder wall 2. Cylinder wall 2 is closedat one end by a cylinder head 5. Cylinder wall 2, piston 3 and cylinderhead 5 enclose a combustion chamber 6.

[0023] A fuel injection valve 7 is situated preferably centrally incylinder head 5. A spark plug 8 is inserted into a borehole in cylinderhead 5 with a slight lateral offset. In addition, at least one intakevalve 9 and at least one outlet valve 10 are also provided. Thearrangement of fuel injector 7, spark plug 8, intake valve 9 and outletvalve 10 is shown in greater detail in FIG. 2.

[0024] In the case of fuel injection system 1 which is in operation, aconical jet of fuel is sprayed into combustion chamber 6 throughboreholes provided in fuel injector 7. A mixture cloud 11 is formed bymixing fuel and air in combustion chamber 6. Mixture cloud 11 is ignitedby spark plug 8. The shape of the conical jet and the recess on sparkplug 8 according to the present invention are described in greaterdetail with reference to FIGS. 3 and 4.

[0025]FIG. 2 shows a section along line II-II in FIG. 1 through theembodiment of fuel injection system 1 according to the present inventionas illustrated in FIG. 1. Fuel injector 7 is situated centrally in arecess 12 in cylinder head 5. Spark plug 8 is situated in a triangleformed by fuel injector 7 and two outlet valves 10. Two intake valves 9are situated symmetrically with outlet valves 10. Intake and outletvalves 9, 10 may also be situated with the sides switched or in a crosspattern.

[0026]FIG. 3 shows schematically a jet pattern of fuel injector 7producing a conical jet of fuel. Fuel injector 7 is situated at thecenter of the circle indicating lateral surface 13 of the cone. Sincefuel injector 7 is designed as a multi-hole fuel injector, multipleinjection jets 14 are sprayed into combustion chamber 6. Injection jets14 are represented symbolically as arrows directed outward. In thepresent embodiment, this is a fuel injector 7 having thirteen injectionholes 16 producing thirteen injection jets 14 accordingly. Individualinjection jets 14 are separated from one another by an angular distanceβ which amounts to 26° in the present embodiment. This does not includeinjection jets 14 a which are injected at the right and left of sparkplug 8. Angle a of an angle cutout 17 between injection jets 14 aenclosing spark plug 8 amounts to 30° to 60° or in the presentembodiment 45°. Spark plug 8 is situated on an angle bisector 18 ofangle α. This arrangement prevents spark plug 8 from being sprayeddirectly by injection jets 14 and 14 a and therefore carbonization ofspark plug 8 can be reduced significantly and the lifetime of spark plug8 can be prolonged.

[0027]FIGS. 4A and 4B show the jet pattern of a second embodiment offuel injection system 1.

[0028]FIG. 4A shows the jet pattern in a top view like that in FIG. 3.Fuel injector 7 is located at the center of the circle representingconical lateral surface 13. In this case, mixture cloud 11 is producedby two different conical lateral surfaces 13 a and 13 b. Angle α ofangle cutout 17 between injection jets 14 a enclosing spark plug 8 againamounts to approximately 45°. Angle β between two injection jets 14which are outside and adjacent to angle section 17, but in thisembodiment are located in two different planes, amounts to approximately20°.

[0029]FIG. 4B illustrates two conical lateral surfaces 13 a and 13 b,which in this embodiment are covered by a total of seventeen injectionholes. The cone angle of internal conical lateral surface 13 b is 90°,while the cone angle of external conical lateral surface 13 a amounts to110°. Internal conical lateral surface 13 b is covered by eightinjection jets 14 while outer conical lateral surface 13 a is covered bynine injection jets 14. This produces a largely homogeneous mixturecloud 11 which does not have any lean pockets.

[0030]FIG. 4C shows a nozzle body 15 of multi-hole fuel injector 7 in aschematic diagram. The injection hole arrangement of nozzle body 15 isshown in a developed view at the side. To create a 45° angle cutout 17,all that is necessary in this embodiment is to omit one of injectionholes 16 situated in a first annular row 19 b, forming internal conicallateral surface 13 b. This in turn produces an angle cutout 17 whichmakes it possible to operate fuel injector 7 without directly sprayingfuel onto spark plug 8. Conversely, a gap may also be provided in thearrangement of injection holes 16 of a second annular row 19 a,producing outer conical lateral surface 13 a.

[0031] FIGS. 5A-5C show diagrams of hydrocarbon and nitrogen oxideemissions and the specific fuel consumption for a fuel injection systemwith and without angle cutout 17 for spark plug 8. The consumption andemission values are plotted here as a function of the firing angle inunits of the crank angle, measured on the crankshaft. The curve shownwith a solid line represents measurement results for a fuel injectionsystem without an angle cutout for the spark plug, and the curve shownwith a broken line with asterisks represents the measurement results fora fuel injection system having an angle cutout for the spark plug.

[0032] In general, the diagrams in FIGS. 5A-5C show that the jet-guidedcombustion method is independent of the firing angle to a great extent.

[0033]FIG. 5A shows the hydrocarbon emissions in volume units for therespective injection systems as a function of the firing angle. Thehydrocarbon emissions decrease significantly when using a fuel injectionsystem having an angle cutout for the spark plug, in some cases as muchas 50% in comparison with emissions in operation of a fuel injectionsystem without an angle cutout for the spark plug.

[0034]FIG. 5B shows a corresponding diagram for the nitrogen oxidesemissions, also plotted in volume units as a function of the firingangle. The emission values for nitrogen oxides remain almost the samefor both fuel injection systems over the firing angle curve.

[0035]FIG. 5C shows the specific fuel consumption for the various fuelinjection systems in units of grams per kilowatt hours as a function ofthe firing angle. Here again, a considerable improvement in consumptionvalues can be achieved by using a fuel injection system having an anglecutout for the spark plug, the reduction in consumption amounting to asmuch as 15% in some cases.

[0036] The present invention is not limited to the embodiments presentedhere and in particular it can also be applied to multi-hole fuelinjectors having fewer or more injection holes. Likewise, the injectionjets may be situated on more than two spray circles (rows) to therebyimprove the homogeneity of the fuel-air mixture.

What is claimed is:
 1. A fuel injection system (1) for internalcombustion engines having at least one fuel injector (7), which injectsfuel into a combustion chamber (6) which is delimited by a cylinder wall(2) in which a piston (3) is guided, and having a spark plug (8) whichextends into the combustion space (6), the fuel injector (7) beingdesigned so that a conical spray jet (13) is produced in the combustionchamber (6), wherein the conical spray jet (13) has an angle cutout (17)in the area of the spark plug (8).
 2. The fuel injection systemaccording to claim 1, wherein the spark plug (8) is situated on an anglebisector (18) of the angle cutout (17).
 3. The fuel injection systemaccording to claim 2, wherein an opening angle of the injection cone(13) is between 60° and 150°.
 4. The fuel injection system according toone of claims 1 through 3, wherein a nozzle body (15) of the fuelinjector (7) has at least one row (19) of injection holes (16) situatedon the periphery.
 5. The fuel injection system according to claim 4,wherein the injection holes (16) situated in at least one row (19) onthe circumference have an angular distance between them amounting tobetween 20° and 30° outside the angle cutout (17).
 6. The fuel injectionsystem according to claim 4 or 5, wherein the injection holes (16)situated on the circumference in a section facing the spark plug (8) arespaced a greater distance apart than those over the remaining angularrange.
 7. The fuel injection system according to claim 6, wherein thegreater spacing of the injection holes (16) to form the angle section(17) is between 30° and 60°.
 8. The fuel injection system according toone of claims 4 through 7, wherein two rows (19 a, 19 b) of injectionholes (16) are situated around the circumference.
 9. The fuel injectionsystem according to claim 8, wherein the two rows (19 a, 19 b) ofinjection holes (16) situated on the circumference are rotated withrespect to one another about a common midpoint (20), so that theinjection holes (16) of the first row (19 b) are situated on the anglebisector of the injection holes (16) of the second row (19 a).
 10. Thefuel injection system according to claim 9, wherein the rows (19 a, 19b) of injection holes (16) which are situated on the circumference andare rotated with respect to one another have an angle cutout (17) in thearea of spark plug (8).
 11. A method of injecting fuel into a combustionchamber (6) of an internal combustion engine by using a fuel injector(7) which is delimited by a cylinder wall (2) in which a piston (3) isguided, with a spark plug (8) projecting into the combustion chamber (6)and a conical injection jet (13) being produced by the fuel injector(7), wherein the conical injection jet (13) has an angle cutout (17) inthe area of the spark plug (8).